In the semiconductor industry, there is a continuing trend toward higher device densities. To achieve these high densities there has been and continues to be efforts toward scaling down device dimensions (e.g., at submicron levels) on semiconductor wafers. In order to accomplish such high device packing density, smaller and smaller feature sizes are required. This may include the width and spacing of interconnecting lines, spacing and diameter of contact holes, and the surface geometry such as comers and edges of various features.
The requirement of small features with close spacing between adjacent features requires high resolution photolithographic processes. In general, lithography refers to processes for pattern transfer between various media. It is a technique used for integrated circuit fabrication in which a silicon slice, the wafer, is coated uniformly with a radiation-sensitive film, the resist, and an exposing source (such as optical light, x-rays, or an electron beam) illuminates selected areas of the surface through an intervening master template, the photo mask, for a particular pattern. The lithographic coating is generally a radiation-sensitive coating suitable for receiving a projected image of the subject pattern. Once the image is projected, it is indelibly formed in the coating. The projected image may be either a negative or a positive image of the subject pattern. Exposure of the coating through the photomask causes the image area to become either more or less soluble (depending on the coating) in a particular solvent developer. The more soluble areas are removed in the developing process to leave the pattern image in the coating as less soluble polymer.
The spacing between adjacent lines of an integrated circuit is an important dimension, and ever continuing efforts are made toward reducing such spacing dimension. The wavelength of light used in the photolithographic process along with the lithographic tool set employed in the process generally dictate the spacing dimension. For example, a tool set designed to provide lines and/or spaces at 0.18 .mu.m does not achieve consistent lines and/or spacing at its minimum range of 0.18 .mu.m but rather is employed to generate lines and/or spacing above the minimum range (e.g., 0.20 .mu.m) with fairly consistent results.
In view of the above, it would be desirable for a technique which allows for a particular lithographic tool set to be employed and achieve consistent lines and/or spacing between lines at the minimum range of the tool set and even below the minimum range.